A novel approach to affinity columns based on the high avidity of biotinylated insulin for avidin attached to solid supports is described. Insulin will be selectively biotinylated at position B1 and the resulting product will be attached noncovalently to avidin-Sepharose. Affinity columns based on this approach will be used for the isolation of insulin receptors from solubilized target tissue plasma membranes. The major aim of this program is the development of high capacity, high affinity columns for large scale isolation studies of insulin receptors.